1. Field of the Invention
This invention relates to catheters and more particularly to multiple concentric catheters having expandable balloons defining a treatment chamber.
2. Previous Art
Blood vessels at certain critical parts of the human circulatory system can and often do become burdened with deposits, coatings, occlusions, and the like (hereafter "burden") which can reduce the vessel's blood carrying capacity. In some patients, this reduced capacity can cause serious and permanent injury. As a result, when significant burden is found to exist, some form of medical intervention is often indicated.
A number of intervention techniques have been developed over the years. These techniques permit the removal or reduction of the burden so that an increased and healthier blood flow can result. When a normal flow cannot be restored by these methods, the burdened portions of the vessel are sometimes bypassed using a vessel taken from elsewhere in the body. When the original blood vessel is a coronary artery, the bypass procedure is referred to as a coronary artery bypass graft.
The bypass graft itself may in time become burdened, as was the original vessel, therefore requiring further intervention. One type of burden that is of particular concern in treatment of a bypass arises when a vein has been used to make the bypass graft. Venous grafts are particularly susceptible to deposits of a friable material which is easily loosened during an intervention.
The friable material is soft and crumbly, and pieces are easily dislodged from the inside of the bypass graft. Often a treatment site will include a high proportion of such friable material surrounding other types of burden. Under these circumstances, attempts to remove the other burden often result in much of the friable material breaking loose and entering the blood stream. This loosened biological debris can move downstream, completely blocking another portion of the artery and causing myocardial infarction.
The intervention techniques referred to above include use of known devices such as balloon angioplasty, rotational atherectomy, the transluminal extraction catheter, stents, directional coronary atherectomy, and the like. Each of these techniques, and others, is favored by practitioners in the treatment of diseased saphenous vein grafts and other vessels. Yet, each of these techniques exposes a patient to some greater or lesser degree of risk of embolism. Unfortunately, this risk is present under the most carefully conducted intervention because the friable material can be so easily dislodged.
The friable material is especially vulnerable to being dislodged from the vessel walls when a catheter is advanced across a region of diseased tissue. Consequently, catheter type treatment devices which must be repeatedly inserted and withdrawn are prone to damage or break loose such friable material. The loosened material, if not trapped in some way, is then carried away in the blood stream.
In treating diseased vessels, it will be desirable to stabilize a treatment site before proceeding with other forms of intervention. The treatment site is "stabilized" by removing as much of the friable material as possible. No current or known device satisfactorily addresses this problem.
Additionally, it is sometimes desirable to administer a medication at a localized treatment site within a vessel. However, the natural biological fluids of the vessel both dilute the medication and carry it away from the region of application.
What is needed is a device for stabilizing a treatment site by removing friable material before other intervention is begun.
Additionally, what is needed is a device for preventing loosened particles of friable material or other plaque burden from entering the blood stream.
There is a need for a device which minimizes the necessity of repeatedly passing a device through a treatment site during the course of an intervention.
There is an additional need for a device which permits a localized application of a medication at a treatment site without undue dilution or the risk of the medication entering the blood stream.